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In the course of fiddling with my alignment, I developed the following method for measuring toe. I found the two keys to accurately measuring toe are the use of slip plates and using as long a measurement baseline as you can. My experimentation with this method shows it has a repeatable accuracy of about 0.05deg within a 95% statistical confidence interval.
Here's what you need
• Laser Level w/ manual beam adjustment - I'm using the Craftsman "4-in-1 Level with Laser Trac" Model No. 320.38251, LM01-002-01-L ($35 at Sears)
• Tape measure
• Scientific Calculator
• Some sort of slip plates - I used two self-adhesive vinyl floor tires with wax paper backings next to each other
• Some tape - I like the using the blue painter's tape

Measuring Toe
• find a level-ish and preferably somewhat shady place to work
• Drive your car on to the slip plates and bounce it a few times
• mark out 36 inches forward of the axle on each side (put a small piece of tape on the ground and make your mark on that
• run a tape measure out about 86+ inches across the car at the 36 inch marks
• with one hand hold the laser level and flush on the hub
• use the projected beam to set the tape measure at 80 inches
• move the other side of the car, position the laser level and flush, and read the tape where the laser crosses - you should be able to read it to the nearest 1/32 inch
• repeat at 36 inches aft of the axle
• Take the difference between the toe and use your calculator to figure out the total toe angle where tan-1[(aft-fwd)/72] = total toe angle

Adjusting Front Toe
The two issues in adjusting your toe are the total amount and a centered steering wheel when you are done. Toe itself is adjusted by changing the length of the tie rods. Make them shorter, the magnitude of toe-in is increased, make them longer and it is decreased.

One full turn of a tie rod will change your toe by about 0.24degrees, which is far more than you will likely need. Accordingly, make toe adjustments in small increments, using the flats and points of the tie rod as points of reference. A one nut-flat turn of the tie-rod will change your toe by about 0.04degrees, which is coincidentally about the limit of what you can repeatably measure. You can make smaller adjustments using the points as a half-turn marker, but you will need to rely on art rather than science at that point. In making adjustments, it's easy to lose your place, so it's a good idea to mark your target flat with a little piece of tape, then adjust the tie rod until that target flat is on the bottom.

The steering wheel becomes off center when the tie-rods are adjusted unevenly, i.e. one is longer than the other. Here's an example of how to fix that -
• The wheel will point towards the side with the shorter tie rod
• The standard steering rack ratio on the E46 is 15.4:1
• So if your steering wheel is off by say 1 deg, this means your wheels are self-centering by 0.06deg
• This in turn means you have a toe differential of about 0.12deg
• The threads on tie rod give you about 0.04deg of toe change per nut flat.
• So lengthen the short tie rod by about 1.5 flats, shorten the long one by about 1.5 flats, and tah-dah - steering wheel is centered.

You can also use this method to measure your total rear toe, but you would need to establish a centerline reference to measure individual toe.

Another quick and dirty way is to put pieces of tape with vertical lines on the trailing faces of each front tire at the height of the wheel center. Drop a plumb line down to just above the ground on each side and measure the distance. Roll the car forward until the tape is at the front at wheel center height and repeat the measurement. If the front measurement is less than the rear you have toe-in. The math of calculating the exact amount of toe is left to the reader.

Another quick and dirty way is to put pieces of tape with vertical lines on the trailing faces of each front tire at the height of the wheel center. Drop a plumb line down to just above the ground on each side and measure the distance. Roll the car forward until the tape is at the front at wheel center height and repeat the measurement. If the front measurement is less than the rear you have toe-in. The math of calculating the exact amount of toe is left to the reader.

I experimented with a few methods and settled on the one detailed above as the most accurate and repeatable.

The two limitations of the method you describe are:

* Repeatability suffers from not using slip plates. You will end up measuring a lot of bushing squirm and consequently have trouble getting the same measurements on repeated trials.

* Accuracy is limited by the short baseline. If you are using a tape measure, +/- 1/32inch is about the smallest increment you can reliably measure. With a 72 inch baseline, this equates to about +/- 0.025deg. But with only a 25inch baseline it works out to about +/- 0.072deg.

In the end though, it is up to the user to decide what level of accuracy suits their needs and how much time and effort they have available to achieve it.

I've found it quite repeatable and excellent for use after changing front suspension components so that you can get the car to a shop for a proper setup.

I think it would work quite well for that.

The motivation in my case was actually having just had an alignment, but being unsatisfied with the front toe settting. It wasn't really the shop's fault, it was a matter of not knowing what I wanted as a result of both an increase in front camber and installation of the stiffer powerflex bushings. Being able to DIY it let me experiment and test with a few different settings to find the one I liked (ended up with zero toe incidentally).